LONDON — Britain is heading for a hung parliament with Prime Minister Theresa May set to surrender a significant number of seats to Labour in the general election, according to a nationwide exit poll for the BBC, ITV, and Sky News.

In what would be an astonishing turnaround for Labour leader Jeremy Corbyn, the number of seats separating the Conservatives from Labour is set to be slashed, with the Tories winning 314 seats and Labour capturing 266.

This would leave the Tories 12 short of an overall majority, if accurate. Labour is up 34 seats on its result in the 2015 election, according to poll, while the Conservatives are down 16. The SNP, meanwhile, are predicted to lose 22 seats.

It’s a shock result that few saw coming, and if borne out seems certain to cause very serious problems for Prime Minister Theresa May’s leadership. She called the snap election from a position of relative strength to try and reinforce the Tories’ lead ahead of Brexit. Instead, she has potentially kneecapped her party.

Meanwhile, Jeremy Corbyn may have defied the critics both inside and outside of the party to grow Labour’s share of the seats compared to 2015.